Is it possible to automatically pass a predefined value to a variable assigned to questdlg, inputdlg, uigetdir (without the input window pop up)?

I am coding a plugin to be used together with a previously existing code (function). The existing code CAN'T be modified. It contains 3 input variables, taking inputs from uigetdir, inputdlg, questdlg. But now the values for these variables are assigned in the plugin code. Hence I need to somehow skip taking those inputs in the previously existing code without making any changes to it.

1. Is there a way to skip executing certain commands? For example, for the code: " a = inputdlg('Input','Title')", if some value is assigned to ' a' previously, this line of code will not execute, and pass on to the next lines of code.

2. Or, is there a way to automatically pass a default (predefined) value when inputdlg / uigetdir / questdlg pertaining to certain variable name is executed. For example for the line of code: " a = inputdlg('Input','Title')", the usual pop up for inputdlg will not happen, rather automatically the value of ' a' will be retained/passed from the previously assigned value.

Answer 1

[Stephen23]

Ugh, this is an unfortunate situation to find oneself in... my commiserations. One possible solution is to shadow those functions: simply use a persistent variable to store the default value, which will be returned when the function is called again. (obviously this is a hack solution, and I advise you to rewrite the original code)

function out = inputdlg(inp,varargin)
persistent val
if nargin==1
   val = inp;
end
out = val;
end

and then call it like this to store the default:

inputdlg(DefaultValue)
... original code here

and then when it is called inside the existing code it will return the default value.

[Asit Kumar]

The inputs from ' uigetdir' and ' questdlg' are assigned to strtures, [e.g.: "handles.store.Hpath = uigetdir(handles.store.homedrive,'Select Path')"].

Ans this line can't be changed. Can structure variables/fields like - 'handles.store.Hpath' declared persistent outside the 'existing code'(function)?

[Stephen23]

@Asit Kumar: I don't understand what "The inputs from ' uigetdir' and ' questdlg' are assigned to strtures" means: did you mean to write that the outputs are assigned to structures?

In any case, I don't really see the relevance to my answer. My answer shows you one possible solution that means you don't need to change those lines in the original code, exactly as you requested.

"Ans this line can't be changed."

I know, your question already made that clear, which is why my answer does not require those lines to be changed. My answer requires defining some new functions and calling them before the original code to specify the default values, like this:

inputdlg(DefaultValue) % Calling my special shadow version!
... your original code here

My answer does not require the original code to be changed. If you do not understand shadowing functions, or persistent variables, or how the MATLAB Search Path works, then some internet searches will give you some useful explanations and documentation, there are also plenty of threads on this forum that will explain these things (the search field is at the top of this page).

"Can structure variables/fields like - 'handles.store.Hpath' declared persistent outside the 'existing code'(function)?"

No.

[Asit Kumar]

Thank you for the clarification :)

[Guillaume]

In my opinion, trying to work around ill-designed code is a fool's errand. The original function was badly designed, UI and processing shouldn't be mixed. It would be better to rewrite the processing part so that it doesn't require UI.

[Image Analyst]

I don't know that it was badly designed, it's just that the original code wanted/expected to ask the user to browse for a file to input rather than pull that name from a file or some other source.

However I agree that it would better just to change the original code to pull the file from some other source, such as a file that was created in advance with all the filenames that need to be included in the batch process.

You could delete the interactive "inputdlg / uigetdir / questdlg" code and replace with code that is more batch job friendly.

Or else change the function arguments to allow a flag that says whether the input is to be batch or interactive so that the function can do it either way.

[Guillaume]

In my opinion, a function that do some data processing shouldn't be in the business of getting the data it processes. It should just have input and output variables and do no I/O. You can then call that processing function from another function that takes care of the I/O. That way, the input can come from the user through input dialog, it can come from a GUI, or a file, or a database, whatever without having to change the processing function.

Separate the UI from the processing is my advice.

[Asit Kumar]

@Guillaume, you're definitely correct, separating UI and processing is a better approach. But for the kind of situation I'm in, I can't make any changes to the existing code because this master existing function is used by numerous other functions. What I'm trying to do is to link my new code to this master function. The flexibility of changing the approach is not there, hence a work around is necessary for the present case.

[Asit Kumar]

@Stephen Cobeldick, With the method you earlier suggested, is it possible to affect the inputdlg command associated with particular variables only ?

For example, suppose there are three occurrences of 'inputdlg' in the code:

a = inputdlg('xxxx');
b = inputdlg('yyyy');
c = inputdlg('zzzz');

Only the assignment to variable 'a' will be automatic (default value assigned earlier: inputdlg(DefaultValue)); but for 'b' and 'c' the prompt will pop up where the user has to enter the values (as it normally happens). Is this achievable? How?

[Walter Roberson]

Create a containers.Map that you populate with variable names and associated value. In your rogue version of inputdlg(), use isKey to check whether the first input is in the container, and if it is then return the associated content; otherwise execute replacement prompting code. (Trying to execute the original Mathworks version when your own has the same name is likely to be a ... challenge.)

[Stephen23]

"Is this achievable? How?"

Inside your function check the input value. Decide what to do based on the value. You will find it difficult to call the original function: you might be able to create a handle to it before shadowing it.

Note that this is an awful hack code and you should rewrite the original code properly.